Polyalkenyl succinic anhydrides are widely used in the petroleum product industry as precursor compounds for the production of hydrocarbyl polyalkenyl succinimides. Hydrocarbyl polyalkenyl succinimides may be used as detergents in fuel mixtures to reduce engine deposits and as dispersants in lubricating oil compositions to aid in the suspension of particulate matter, additionally having the property of modifying the fluidity of a lubricating oil composition. An example of a polyalkenyl succinic anhydride suitable as such a precursor compound for making lubricating oil additives is polyisobutenyl succinic anhydride (“PIBSA”). PIBSA is usually produced by following either of two conventional processes. For the purposes of simplicity, reference will be made to the process for PIBSA, however the disclosure is intended to relate to processes for the production of all hydrocarbyl polyalkenyl/acid compounds not just PIBSA.
The first process consists of a direct thermal condensation reaction between maleic anhydride and polyisobutene (“PIB”) and is often referred in the art as the “thermal ene” reaction. In the thermal ene reaction, a carbon-carbon bond is formed between an alpha-carbon on the unsaturated organic acidic reagent and a vinylic carbon at a terminus of the polyalkene. Sustained exposure to elevated temperatures above 150° C. is required to obtain good reaction yields, usually for a time period ranging from about 1 to about 48 hours. However, high reaction temperatures typically lead to the formation of a sedimentous resin which is believed to be due to the polymerization and/or decomposition of maleic anhydride. The formation of such insoluble resin or sediment in significant amounts requires a filtration stage before the PIBSA can be used as an additive or as an intermediate in the preparation of other products such as hydrocarbyl succinimides. Furthermore, according to U.S. Pat. No. 5,644,001, undesirable resins in the product introduce not only a significant discrepancy between the real and apparent succinylation in the maleinised product (due to the presence of resinified and/or unreacted maleic anhydride) but also adversely affect the detergency properties of such additives.
In the second type of process, chlorination of the PIB is first carried out, followed by the condensation of the chlorinated PIB with maleic anhydride. This process can be carried out at lower temperature than the thermal ene reaction process, with high yield and without the formation of substantial amounts of sediment. However, the PIBSA obtained with this process contains residual chlorine. Environmental concerns related to chlorine-containing materials and the potential for formation of hazardous byproducts, such as dioxins, that may arise under the conditions prevalent in an internal combustion engine make the use of the second process undesirable. Furthermore, chlorine is also known to be a poison for the catalysts used for exhaust gas treatment systems, i.e. as in catalytic converters.
The aforementioned conventional methods for the preparation of PIBSA tend to involve side reactions that produce tars, resins, or halogenated byproducts which must be separated from the PIBSA before further processing occurs. Undesirable resinous byproducts and reduced product succination are more prevalent when the ene reaction is conducted at elevated temperatures and the polyalkenyl compounds have number average molecular weights above about 1200. Accordingly, there remains a need for an improved synthesis process for relatively highly succinated polyalkenyl succinic anhydrides of relatively high number average molecular weight that does not produce undesirable byproducts during the course of the reaction and does not require extreme reaction conditions such as prolonged heating, elevated pressure, or the presence of a strong acid.
In accordance with a first aspect, an exemplary embodiment of the present disclosure provides a process for making a polyalkenyl succinic anhydride, such as PIBSA. A mixture of highly reactive PIB and maleic anhydride are heated until at least about 50 weight % of the PIB is converted to PIBSA. An additional amount of maleic anhydride is added to the mixture which is subsequently contacted with chlorine gas to convert at least some of the unreacted PIB to PIBSA under conditions sufficient to inhibit the formation of undesirable resinous or chlorinated byproducts.
In accordance with a second aspect, another embodiment of the present disclosure provides a hydrocarbyl succinimide made from a PIBSA produced by the aforementioned process.
In accordance with a third aspect, a further embodiment of the present disclosure provides a lubricant component comprising a hydrocarbyl succinimide made from a PIBSA produced by the aforementioned process.
As described herein the disclosure provides a two-step process for the preparation of polyalkenyl succinic anhydrides, such as PIBSA, with the resultant product having a relatively high ratio of succinic functional groups to polyalkenyl functional groups, and a relatively low level of undesirable contaminants. This novel process also allows PIBSA with a number average molecular weight greater than about 1000, and up to about 3000, to be synthesized. Higher number average molecular weight and a higher ratio of succinic groups to polyalkenyl groups in a compound such as PIBSA increase the dispersant performance of a dispersant made from the PIBSA when the dispersant is combined in a lubricating oil mixture. Accordingly, a smaller amount of dispersant additive may be used per quantity of lubricating oil composition, thereby reducing the cost of production of the lubricant composition as well as reducing the environmental impact.